Some printing systems form a printed image by ejecting ink from ink printheads. Thereby, ink is applied onto a print medium for printing a pattern of individual dots at particular locations. The printed pattern reproduces an image on the printing medium. At least some of these printing systems are commonly referred to as inkjet printers.
A fixer fluid may be used for improving print quality of a printed pattern. In particular, a fixer fluid may address coalescence, bleed, or similar effects characterized by ink or pigment migration across a printed surface. A printing system may include a treatment printhead configured to eject a fixer fluid over the print medium. The treatment printhead applies the fixer fluid by ejecting the fixer over the particular locations for ink placement. Thereby, the fixer treats ink on the print medium in order to address the above mentioned effects. The fixer fluid may be applied before, after or, quasi-simultaneously to the application of the ink.
Some printing systems implement automatic sensing of fixer fluid applied on a print medium. Automatic sensing of fixer on the print medium may facilitate determining whether: a) a particular treatment printhead ejects, in fact, fixer fluid; b) the treatment printhead applies fixer fluid at selected nominal positions; and/or c) the treatment printhead applies fixer fluid at selected nominal densities or flow volumes.
An optical detector may be configured for sensing fixer fluid applied to a print medium. However, sensing of a fixer fluid applied on a print medium can be challenging. For example, optical detectors may have a too low sensitivity for suitably detecting fixer fluid on the print medium.